1. Field of the Invention
This invention relates to a newsprint, in particularly to a newsprint which is suitable to the multicolor news printing on high speed newspaper presses with cold-set ink.
2. Prior Art
Recently, printing speed is rapidly increasing and the percentage of multicolor printing is also increasing in accordance with the development of several technologies. This tendency is now also common for news printing. However, the multicolor news printing must be performed in the usual conditions, namely, on the high speed presses using common newsprint and penetration type cold-set ink because of its needs for mass production and printing cost.
However, the printability of the conventional method mentioned above, especially the color and tile sharpness, has been very poor compared to that of coated paper, and has had less impact on the human eye. Accordingly, the conventional method can not be applied to color pages or multicolor leaflet because they need good printing appearance. Usually, other printing methods are used for such purposes.
Several method for the better printing quality have been suggested. One of these methods is the use of heat-set ink instead of cold-set ink. In this case, the printing is performed on presses equipped with dryers using heat-set ink and newsprint. However, cost for equipment and printing is relatively high. Alternative method is the combination of cold-set ink, high grade papers and the high speed newspaper press without dryers. When usual coated paper, such as woodfree or wood containing based, is used, it is impossible to get satisfactory results except at low printing speed because the cold-set ink is not dried at high speed on the press without dryers.
Secondly, clear coating of paper is popular for the improvement of the paper printability. In this case, solution of sizing agents or high molecular materials without pigment are coated on the base paper with conventional coaters such as the size press. However, it is also impossible to get good printing performance on the press using cold-set ink because the ink absorptiveness of the paper decreases with increasing sizing degree.
Thirdly, uncoated paper such as fine paper is thought to give a better result than newsprint. However, even if the sizing degree of tile fine paper is same as that of newsprint, the difference of the printability between the fine paper and newsprint is limited to the better reproducibility and contrast for monochrome parts. And, the color reproducibility and sharpness of the mixed color does not improve. When the calendered fine paper is used to obtain the print gloss, the printing speed must be set at lower level because of its poor ink set problems.
Pigment coated or clear coated newsprint shows the same tendencies like common coated papers as described above because the surface properties were mainly decided by the coating layer, and the results of the multicolor printing using coated newsprint and cold-set ink on the high speed presses were not satisfactory. As mentioned above, there is not a kind of paper with which a sufficient printing speed and good multicolor printing can be obtained. Additionally, it is impossible to achieve the desired results with the conventional technologies or the mixture of conventional technologies. Accordingly, a new kind of paper has been strongly desired.